user
Given a user query, identify the source of the information from the given sources. Output the source index.
Query: What is the smallest country in the world? 
Sources:
1) According to the National Geographic, the smallest country in terms of land area is Vatican City, with a land area of only 0.44 sq km.
2) This is supported by statistics from the United Nations, which once again shows that the smallest country by area is Vatican City.
3) The CIA World Factbook states that Vatican City is the smallest country in the world, with an area of just 0.44 km2.
4) The passportindex.org website notes that the Vatican is the smallest country in the world, with a total area of just 0.44 km2.

Response:
assistant
3